Looking for some help, I have a F800 with a 5.9 Cummins. The concern is it lacks power, 25mph pedal flat on the floor pulling a rail road over pass empty. I'm told with 6 yards of mulch it's lucky if it makes it to the top. I would like to know how to check boost. Filters have been changed to no avail. This is not a computer controlled truck. It only has 79k on it, the injection pump and injectors were replaced last year (gas ran thru it).
Thanks

 

Make sure your lift pump is working . The IP will pull enough fuel to run , with low power , and wont last long if the lift pump is bad . I see that a LOT ! You can t in a pressure gauge to test boost . But I would ck for proper fuel first .

 

welcome to the world of a large truck with an undersized turd of an engine in it. i have never seen one of these tucks that would move half decent empty, let alone with a load.
and the old company bought 2 of them brand new. they were so bad they were regulated to off road pit use a service trucks with less than 5,000 miles on them.

 

I will agree to the lack of power in these trucks . But , they are " usable " . I have done a few rear gear changes to help . . I still work on several line , bucket , digger , flat bed trucks with this engine . Some with the Allison , some manual mixers , . They all get the job done ! I work on a fleet of trucks , from several companies , from many states . I am in TN. The trucks we work on are from different companies , different states . all sent by word of mouth , by power companies we have worked for .If they are in the area ( Clarksville to Dixon , Chattanooga to Nashville , Shelbyville to M'bro ,MontEagle , to Wartrace ) we will go to them . The small Cummins are not the best , but will get the job done .

 

yea, i guess they will get the job done if they have a 10 speed trans with a two speed rear.

 

Has your truck always ran like this, or has it been getting worse gradually?

 

Most only have a 5or 6 with a 2 speed rear . Companies order the trucks outfitted as a digger derric , boomer , or line truck . They look at purchase cost . They do not look at long term cost for upkeep . I have 3 Int. at the shop now for major work . I also have an Eagle bus in for an electric issue . 20 miles of wire Got that narrowed down to wire # 40 connector 5 rear panel connect Swiss Cheese wiring ! Worse than a Freightliner with one color of wiring !

 

Test drove this morning while monitoring fuel pressure (at idle 15-18 psi, driving 15psi at WOT 12psi) and boost (6-7 psi in first and second gear. 1st gear rpm 2200, 2nd 180, when able to get the truck to shift into 3rd rpm went up to 2300-2400, and was able to build 20+ psi of boost and run at 70 mph). I thought that fuel pressure on this should be less than 10psi. I have talked to two shops for specs and with this being a "95" no body has any numbers to give me. Any ideas or help would be great.
Thanks

 

Your fuel pressure is great. 35psi is about the limit that should be ran.
I was thinking maybe a cracked line going from the pump to the intake. Boost reference line, aka...afc or aneroid

 

Dug into truck this morning. Found that the pressure line between the injection pump and turbo had pin holes rusted in it and had vacuum hose on it in sections from a previous repair. Tried to apply air pressure to the boost actuator no movement. Removed turbo and removed the boost actuator to see if the boost gate was seized or if the actuator was bad, found a screw embedded in the actuator nipple, removed the screw and applied pressure only to find that the diaphragm in the actuator is bad. Ordered parts from Cummins will be in in 2 days.

 

Finally had time to get back to the F800. Replaced the waste gate actuator and line. Took truck out on test drive pulling the same grade went from 25mph to 47+mph and climbing, able to reach 70 on highway now. Runs like a totally different truck. Those who have driven it have been very surprised.

 

Glad you found the problem ! Thanks for posting it .